/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Supplier;
import java.util.concurrent.Callable;
import javax.annotation.Nullable;

/**
 * Static utility methods pertaining to the {@link Callable} interface.
 *
 * @author Isaac Shum
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Callables {
    private Callables() {}

    /**
     * Creates a {@code Callable} which immediately returns a preset value each time it is called.
     */
    public static <T> Callable<T> returning(@Nullable final T value) {
        return new Callable<T>() {
            @Override
            public T call() {
                return value;
            }
        };
    }

    /**
     * Creates an {@link AsyncCallable} from a {@link Callable}.
     *
     * <p>
     * The {@link AsyncCallable} returns the {@link ListenableFuture} resulting from
     * {@link ListeningExecutorService#submit(Callable)}.
     *
     * @since 20.0
     */
    @Beta
    @GwtIncompatible
    public static <T> AsyncCallable<T> asAsyncCallable(final Callable<T> callable,
            final ListeningExecutorService listeningExecutorService) {
        checkNotNull(callable);
        checkNotNull(listeningExecutorService);
        return new AsyncCallable<T>() {
            @Override
            public ListenableFuture<T> call() throws Exception {
                return listeningExecutorService.submit(callable);
            }
        };
    }

    /**
     * Wraps the given callable such that for the duration of {@link Callable#call} the thread that
     * is running will have the given name.
     *
     *
     * @param callable The callable to wrap
     * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called
     *        once for each invocation of the wrapped callable.
     */
    @GwtIncompatible // threads
    static <T> Callable<T> threadRenaming(final Callable<T> callable, final Supplier<String> nameSupplier) {
        checkNotNull(nameSupplier);
        checkNotNull(callable);
        return new Callable<T>() {
            @Override
            public T call() throws Exception {
                Thread currentThread = Thread.currentThread();
                String oldName = currentThread.getName();
                boolean restoreName = trySetName(nameSupplier.get(), currentThread);
                try {
                    return callable.call();
                } finally {
                    if (restoreName) {
                        boolean unused = trySetName(oldName, currentThread);
                    }
                }
            }
        };
    }

    /**
     * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that
     * is running with have the given name.
     *
     *
     * @param task The Runnable to wrap
     * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called
     *        once for each invocation of the wrapped callable.
     */
    @GwtIncompatible // threads
    static Runnable threadRenaming(final Runnable task, final Supplier<String> nameSupplier) {
        checkNotNull(nameSupplier);
        checkNotNull(task);
        return new Runnable() {
            @Override
            public void run() {
                Thread currentThread = Thread.currentThread();
                String oldName = currentThread.getName();
                boolean restoreName = trySetName(nameSupplier.get(), currentThread);
                try {
                    task.run();
                } finally {
                    if (restoreName) {
                        boolean unused = trySetName(oldName, currentThread);
                    }
                }
            }
        };
    }

    /** Tries to set name of the given {@link Thread}, returns true if successful. */
    @GwtIncompatible // threads
    private static boolean trySetName(final String threadName, Thread currentThread) {
        // In AppEngine, this will always fail. Should we test for that explicitly using
        // MoreExecutors.isAppEngine? More generally, is there a way to see if we have the
        // modifyThread
        // permission without catching an exception?
        try {
            currentThread.setName(threadName);
            return true;
        } catch (SecurityException e) {
            return false;
        }
    }
}
